Building ebike battery pack with Ryobi P108 (4AH) 18v

Hello all! First post.

After reading a lot and not finding all that much about specifically using the P108 Ryobi 18v 4AH batteries to make a pack (except for one thread where someone mixed it with greenworks batteries http://endless-sphere.com/forums/viewtopic.php?f=14&t=56505), I decided to just go for it and document it here! *edit* I have since been discussing the use of these batteries with bluovalguy on his thread and running other side tests if you want to know more about these.

So here is my setup:
-4x 18v 4AH (2x2 series/parallel); cost 99$ for the first pair and 129$ for the second (average 57$ a peice)
-4x ryobi fuel gauge as the connector (sale for 12$ each) (actually 6 of them because of the sale, but only using 4 of them at this moment)
-*** this step is done, gear updated***a Strong branded bike with SLA battery (the thing weighs over 40kg) that I got used. It certainly gets the job done, but I would like to eventually be able to use my regular commuting bike as electric OR bare with no extra weight, so I hope that in changing parts slowly I can get a setup I like and then transfer it over to my normal commuting bike as a front-wheel drive once everything is ready.
-***new setup*** I am now waiting for my outbound 02 motor from ebikes.ca; I will mount it in an alex rims DM18 with a wide tyre to add traction, with the computer and 20 AMP controller, on a Kona dr. good with 8-speed nexus hub in the back (so the bike I've been commuting with for a few years).

Why this setup? Simple, I can't get this many reliable cells that I don't need to solder (soldering aluminum is too sketchy on the cells, I don't like it) for this cheap, and it is also hard to get readily available chargers and extra packs if one cell dies. This way I only need to replace 1/4 of the pack at a time if a cell is defective, and I can easily keep chargers at work and at home if I need it (for now I have 3 at home already). Not only that, but since I use lots of these tools, I also have spare 1.2AH batteries laying around if I want to go super light-weight for short hauls (or just one pair of the 4AH if I want that). It seems like a very flexible and affordable option. So far I have spent under 300$ on the pack, and the chargers just came with my tools and a spare would be easy to get (60$ for the 6x charger if I go cross border shopping).

Progress:
July 3rd
-So far I have made the connectors for the batteries. Sometime this weekend I hope to take the bike out for a ride.]
-I used the fuel gauges based on the recommendation of bluovalguy, and it works. I can measure the voltage just fine when the fuel gauge is on, whereas this is not true when I try to measure the battery directly (as had been reported by bluovalguy).

July 4th
-No-load test in the house successful (the bike upside down).
-The batteries normally turn on properly, but as I played with the harness and put and removed the batteries multiples times, every now and then a battery did not "sync" (as bluovalguy had put it). I can't replicate the issue and it seems to move around, but simply removing the batteries and putting them back in fixes it.

July 5th
-The pack is now built and fully secured/ready to use
- Took it out for a very short spin (1 minute), packs some puch! What an upgrade over SLA!!!! Now all I need is an endurance test (well along with making a proper bag for the batteries because yanking them out of a backpack by the wire harness is only going to work a few times )

July 16th
-got the parts, ordered new rim, waiting for the rest of the parts for assembly.

More to come!

Bikes draw 4 to 6x the amps of a drill. So you might need to consider 12 ah, lest you prematurely wear out your cells.

But if your bike is a weak 250w one, then 8 ah pack will do.

Thanks for the input! My current bike is a 200w motor and for my future conversion of my commuter bike I am thinking a geared front hub, and am currently looking at the Outrider (I had previously wrongly called it a 9c)

http://www.ebikes.ca/shop/conversion-kits/geared/front-mini-geared-kit-advanced-pas.html

and the BMC

http://electric-bikes.com/betterbikes/bmc.html

(I was also looking at this guy http://gocarlite.com/Electricbikekitproducts.php?view=productPage&product=3 but it seems too good to be true, and I prefer reliability so I won't consider it unless people can chime in about it)

But yes, eventual 12AH if everything works would be the next step, but for now I figured 8AH was enough to test everything but that 4AH would probably not be enough for the tests (so I tried to minimize cost risks for the testing phase). Also the P108s are supposed to be able to be run at 7.5c per cell (so 15c for the pack). Also, given that the p108 are 2.8 more amps than standard battery packs for the drills, and that I use 2, I already reach that 6x more power than what the drill requires, so even by the 6-8x more power standard you set out, these packs should be able to handle it (although I do agree that having extra overhead is always the best way to go, especially with batteries).

But that brings up a question I had actually... If I go with a high-speed winding, will my motor draw more current? How many AMPS should I be aiming for for the kind of motors I am looking at? Won't the controller limit the current at 20-25 amps (depending on what I set) and so keep the battery at under 3c? I do have large hills on my ride (1.5-2km of pretty steep hill).

*edit, I had previously stated 11c capacity, I meant to report the continuous discharge value, not the peak; it should have read 7.5c, which is still more than enough, although it is rated as capable of 11c, most spec sheets rate it at 7.5c because at 11c it is also rated for 250 charges at 60% capacity, which is a pretty expensive way to waste batteries IMO!*

can't generalize on tool packs. some are cheap low C like dogman owns, others like yours are 11c.
i derate by 50%. so your 88a dual packs i rate only 40a.
but with a 25a controller, if that is peak pulling away from a stop, 25a, that is a good match. should not decrease life at all.
That is only 6.25a per cell on a 22a mfg C rating. it won't even get warm.
But on hills, 4 packs won't take long to need a charge if you pull 25a. time to head home in just 15 minutes of pikes peak.

Thanks. And I know it can do it because I also have a portable miter saw that drains the battery in less than 10 minutes and the packs fair well, so they can handle the drain.

That being said, do you know how winding impacts the amperage requirement for a same amount of torque?

first post updated with progress.

I have always thought that those portable tool batteries would make a great lower wattage setup because they are easy to get, low cost and chargers are fast. Good for short commuting.

BYqSXt8Z said:

That being said, do you know how winding impacts the amperage requirement for a same amount of torque?

Click to expand...

Can`t really comment on torque but try this on for size.
Motors wound for high speeds will draw more amps longer than a motor wound for low speed. I have a few 9c motors with different windings slow 6x10, mid 9x7, fast 12x5. The fast wound motor 12 wires x 5 turns when run with the same battery pack and controller as the other motors will cause the controller to heat up much more.
BEMF or some other invisible concept comes into play as a motor reaches it`s max speed. As a motor gets up near max speed bemf starts to regulate current flow. A slow wound motor will self regulate at a lower speed compared to a fast wound motor. I call the 12x5 an amp hog as it will pull more amps for a longer time trying to get up to it`s speed. With a high speed motor the battery controller and wires, need to be built to provide more amps.
As Dogman has stated many times a slow motor with more volts is a very nice way to power an e bike.

Icewrench said:

BYqSXt8Z said:

As Dogman has stated many times a slow motor with more volts is a very nice way to power an e bike.

Click to expand...

Click to expand...

Thanks! I plan on respecting the 32kph (20mph) max on flat (provincial laws), I am more concerned with keeping speeds up on the hills and in the wind (so when there is more resistance). I think the slower wound motor is better for be in that respect, but I am just checking. I also wrote the the store owner, so we will see what he has to say about torque. Also based on my reading in the past days, I am pretty sure that higher speed motor = less torque.

However, since I am using 18v packs means I can either do 36v or 54v, and most controllers (and I assume motors) are rated at 48 max. unless you jump to 72v

A motor will take any voltage that is fed to it. Volts determine the max speed the motor will spin.
Controllers are voltage sensitive. Limited by the volt rating of the capacitors and mosfets that it is built with.
Most of the common 36 volt controllers are built with 63 volt caps and maybe 75 volt fets. So they can handle a 48 volt pack that might actully have a max charge of near 60 volts.

Have fun.

Icewrench said:

A motor will take any voltage that is fed to it. Volts determine the max speed the motor will spin.
Controllers are voltage sensitive. Limited by the volt rating of the capacitors and mosfets that it is built with.
Most of the common 36 volt controllers are built with 63 volt caps and maybe 75 volt fets. So they can handle a 48 volt pack that might actully have a max charge of near 60 volts.

Have fun.

Click to expand...

hahaha so my 54v pack would really be pushing it. The p108s fully charged output just shy of 21v each; it woudl be just over 62v just shy of 63v.

I went ahead and ordered this fella http://www.ebikes.ca/shop/conversion-kits/geared/front-mini-geared-kit-advanced-pas.html so the endurance test will have to wait two weeks + build time, but I am looking forward to it. So I guess this thread will be kind of dead for a bit now.

dogman said:

Bikes draw 4 to 6x the amps of a drill. So you might need to consider 12 ah, lest you prematurely wear out your cells.

But if your bike is a weak 250w one, then 8 ah pack will do.

Click to expand...

Hey dogman, I just wanted to apologize for mistakenly stating that the continuous discharge current of the cells is 11c, it is in fact 7.5c (so 15c per pack). It still stands that these cells should be more than sufficient for my use on a small commuting setup (on a 20 amp controller), but I don't want anyone burning through them because they tried to use them on a 40 amp per pack setup thinking they still had a 10% overhead.

Here are the spec sheets.
http://www.candlepowerforums.com/vb/showthread.php?371882-Test-Review-of-Samsung-INR18650-20Q-2000mAh-(green)
http://www.batterysupports.com/samsung-18650-inr1865020q-2000mah-36v-15a-liion-battery-cell-p-24.html

*edit*

Ahh! sorry for spamming my own post! I found the sheet that had the 11C value. 7.5 is a much better value, as although it can take 11c, it is doing so with a life cycle of 250 recharges at 60% capacity.... so I would never want to run it that high for extended periods of time. There was another thread on the forum that showed that at about 2c use, after 250 cycles it was only down 6% instead of the 40% the specs sheet of 11c (I have to find it again).

http://www.avacom.cz/Datasheety/Samsung/INR18650-20R.pdf

Finally tested!

The results are ambiguously successful. The current smoked a part of the meter (don't know what part yet, will open them), but the harness as a whole kept working just fine. Conclusion: the batteries can be used to run an e-bike with a harness of "fuel gauges", but the fuel gauges will smoke on first use.

Will update first post once I am done diagnosing the fuel gauge.

BYqSXt8Z, great thread. It's got a lot of useful info for something I'm planning on doing w/ the Ryobi P108's as well. Any update on longevity testing w/ these batts?

My apologies, if I'm raising this thread from the dead.

Drivesolo said:

BYqSXt8Z, great thread. It's got a lot of useful info for something I'm planning on doing w/ the Ryobi P108's as well. Any update on longevity testing w/ these batts?

My apologies, if I'm raising this thread from the dead.

Click to expand...

As had been pointed out, some of the batteries and readers don't play so nicely with parallel pack setups without making sure they all get actiavted at the same time, but in series, it is very easy. If you are using battery meters like I had pointed out, do expect some of them to burn out (the ones that are downstream of a larger pack will overload, don''t worry about it, it changes aboslutely nothing to their function as a socket for the battery, it only burns out the meter part)

I used the pack successfully for my test rides, but by the time I was fully up and running I had also built meself a headway HP pack, so I canabilized the ryobi pack to make multiple small packs to make other things. For example, I am now using a p108 as a replacement pack for a powerwheel; much simplet given that it only needs one battery as-is.

^ It's funny you should mention using the P108 for a Power Wheels. I swapped out the 12V batt form my daughter's Power Wheels when it was running down. That's what got me to thinking about how simple it would be to use the P108s that I currently have for other purposes which I have but only individually or two in series . Since the dual pack of P108s (P122) has recently dropped to $89 at Homedepot, I have more interest in them now provided I can make everything work in parallel packs.

What I'm mulling over is how to keep all the packs in a parallel setup awake while the current draw form the whole battery pack is idle. Do the LEDs on the fuel guage serve that purpose? Did you ever encounter problems of batteries going to sleep (8V) during the time that you used them?

Drivesolo said:

^ It's funny you should mention using the P108 for a Power Wheels. I swapped out the 12V batt form my daughter's Power Wheels when it was running down. That's what got me to thinking about how simple it would be to use the P108s that I currently have for other purposes which I have but only individually or two in series . Since the dual pack of P108s (P122) has recently dropped to $89 at Homedepot, I have more interest in them now provided I can make everything work in parallel packs.

What I'm mulling over is how to keep all the packs in a parallel setup awake while the current draw form the whole battery pack is idle. Do the LEDs on the fuel guage serve that purpose? Did you ever encounter problems of batteries going to sleep (8V) during the time that you used them?

Click to expand...

I haven't had any packs go off once properly activated, as long as I pulled current from it. If you let it idel too long it will turn off. The LEDs on the meter can indicate that the pack has been activated, but even when the LEDS burn out the connectors still work, you just have to trust your method though because the visual indicator is gone... So I recommend some testing and practice with a volt meter before using it on the bike so you know the pattern of turning on and off your batteries well.

I have been wondering if the "test" button on the batteries could be used to wake them, this did not seem to work for me when I tried.

A little while ago I did a quick check of the P108, if I recall correctly, this is what I found:
- Once awaken it seems like it will stay on for more than a minute even when there is no current draw as long as it is hooked up to a multi-meter measuring it's voltage.
- Once current draw is stopped and checked w/ a multi-meter periodically it seems that it only stays awake for about 20 seconds.
- Pushing the status button only seemed to briefly wake up the batt for several seconds after the light goes out.